Heteroepitaxy of wide band gap semiconductors on silicon substrates

The wide band gap semiconductors SiC and GaN have shown great potential for use in high-temperature, high-power and high-frequency electronic devices as well as short-wavelength optical devices. However, the lack of large-area and low-cost substrates hindered their development seriously. Thus, the heteroepitaxy of SiC and GaN on silicon substrates is highly desirable for the Si-based electronic industry. In this study, we investigated the epitaxy of 3C-SiC and hexagonal GaN on silicon substrates and related devices. For 3C-SiC growth, a carbonization process was adopted and optimized in order to obtain single-crystal 3C-SiC epilayers on silicon substrates using trimethylsilane and silane/propane precursors, respectively. The thick 3C-SiC films grown on Si(100) substrates are potentially used for 3C-SiC device fabrication while the thin 3C-SiC films grown on Si(111) substrates are used as a compliant buffer layer for GaN epitaxy. The 3C-SiC device fabrication processes, including ohmic contacts and gate oxidation, were developed and inversion-mode n-channel 3C-SiC MOSFET's were fabricated. These devices exhibit excellent transistor characteristics and a channel mobility of 165 cm2/Vs. For GaN growth, AlGaN/GaN heterostructures were grown on 100 mm diameter Si(111) substrates using a high-temperature AlN buffer layer. The effect of AlN deposition conditions on AlGaN/GaN quality was investigated. To prevent GaN epilayers from cracking, a 3C-SiC/AlN composite buffer layer was employed to achieve 1.4 mum-thick crack-free GaN epilayers. In addition, the growth of hexagonal GaN on Si(100) substrates was demonstrated using a sputtered AlN buffer layer followed by a MOCVD grown AlN buffer layer.